It might run with a .281" insert, but that's awful big for
stunt purposes. My .25LA venturi is drilled out to .272" with .156" (K&B) spraybar. That's pretty large for a .25, which is itself roughly 25% bigger in displacement than a .19 (most .19's are .199 CID). I only did that because I was going to fly it in Reno at 4,900' elevation. I would suggest starting with .257" or .265" if you're interested in stunt or sport flying the .19. Also, remember that you can make the venturi "smaller" with multiple layers of pantyhose material. How you get the pantyhose material is best left unmentioned.
Steve